There is a type of LED illumination in which light from an LED is guided into a light guiding body and at the same time, the light is diffused to the outside by a diffuser included in the light guiding body. Particularly, if a curved shape is provided in the light guiding body, added value can be increased as design illumination. A curved surface can be approximated by an R shape (a circular shape in a certain cross section) in a local region.
For example, Patent Literature 1 is known as an example of a case in which a light guiding body has an R shape. An LED is used as a light source and light from the light source is guided into a light guiding body by using a metal reflector. By adopting such a structure, direct light from an LED can be blocked by the reflector. Thus, glare of direct light can be reduced. However, the metal reflector absorbs about 10% of light in one reflection. Thus, a lower light output ratio results.